Passing environmental variables to library?

I’m calling a C library FastTransforms (https://github.com/MikaelSlevinsky/FastTransforms) whose threads are controlled by two environmental variables:

export OMP_NUM_THREADS=4
export VECLIB_MAXIMUM_THREADS=4

If I call an executable from the command line, the library sees the settings and correctly launches 4 threads. If I call the library from within Julia via ccall, it is only launching 1 thread.

Any ideas how to correctly “pass through” the environmental variables?

One idea is to try the Base.ENV which seems to be an interface to environment variables of the current process. If this feeds through via dlopen to the library is tbt.